386 



THE IMPERFECTION OF THE 



upon the denuded surface of the Chalk, filling up all the inequalities 

 of its eroded surface. 



Section, showing strata of Tertiary age (a) resting upon a worn and denuded surface of White^ 

 Chalk, (b) the stratification of which is marked hy lines of flints. 



In the unconformability, then, between the Chalk and Eocene 

 Rocks, "we have unequivocal evidence — irrespective of anything that 

 ■we learn from Palseontologj — that the break between the two forma" 

 tions was one of enormous length. In Britain, the interval of time 

 thus indicated is not represented by any deposits, and in Europe 

 generally, there are but a few fragments of such. We may be quite 

 sure, however, that during the time represented in Britain by the 

 mere line of unconformability between the Chalk and the Eocene, 

 there were somewhere deposited very considerable accumulations of 

 sediment. "Whether we shall ever succeed in discovering these, or 

 any part of these, is, of course, uncertain. We may be certain, how- 

 ever, that such deposits, if ever discovered, will prove to be charged 

 with the remains of animals intermediate in character between those 

 of the Cretaceous and the Eocene period, and the large gap now 

 existing between these formations will thus be more or less com- 

 pletely bridged over. 



Amongst other well known instances of more or less general 

 unconformity in the stratified series, may be mentioned that between 

 the Lower and ITpper Silurian (not always present), that between 

 the Lower and Upper Old Red Sandstone (also not universal), that 

 between the Carboniferous and Permian Rocks, that between the 

 Permian and Triassic Rocks (not universal), and that between the 

 Lower and Upper Cretaceous Rocks. All these physical breaks are 

 accompanied by more or less extensive palseontological breaks as well. 

 Other breaks which the absence of fossils renders less important, 0£ 



